RWLeu-4 in a recently established, Philadelphia chromosome positive (Ph1) cell line isolated from a patient in the "blast phase" of chronic myelogenous leukemia (CML). Treatment of RWLeu-4 with la,25(OH)2 Vitami D3 (1,25-D3), phorbol esters (PMA), or DMSO causes these cells to cease proliferating and to differentiate into cells with phenotypic, functional, and cell surface antigenic characteristics of monocytes and/or macrophages. We have recently derived a variant of this cell line, designated RD3, that in resistant to the anti-proliferative effect of 1,25-D3 but in still induced to differentiate in response to these agents. Using both the wild type and the resistant cells, we will investigate the mechanism of anti-proliferative action of 1,25-D3 on these CML cells. We propose to characterize the 1,25-D3 receptors in bc RWLeu-4 and RD3 cells using DNA-cellulose elution profiles, partial peptide maps, and DNA-cellulose binding profiles. If differences are found, we will further characterize the genes coding for the receptors using molecular cloning techniques. If no differences are found we will examine changes in other signal trasduction systems such as protein kinase C and other protein kinases, phosphatidylinositol metabolism interferon, cyclic nucleotide production and changes in the phospholipid, content of the cell membrane. Exploiting differences in gene expression in RWLeu-4 and RD3 in response to 1,25-D3 as detected by differential hybridization of cDNA's made from treated and untreated rwleu4 and rd3 cells, we will investigate the factors specific for the regulation of proliferation per se. By doing so, we hope to further understand the processes that prevent normal maturation of cells in CML and begin to elucidate the factors that regulate cellular proliferation. Furthermore these studies will enhance our understanding of the mechanism of action of 1,25-Da in general, and regulation of proliferation and maturation in hematopoietic cells in specific.